1. Field of the Invention
The present invention relates to an image processing apparatus and, more particularly, to an image processing apparatus which performs pixel density conversion processing, spatial filtering processing, contrast processing, and the like for color image data.
2. Description of the Related Art
In conventional image processing apparatuses that perform image editing and image transmission, the image data to be processed are encoded upon storage or transmission, thus realizing reductions of the memory capacity and the transmission data volume.
In such conventional image processing apparatus, many encoding schemes of image data have been proposed and put into practical applications. Of such encoding schemes, the method of compressing color image data in the YUV (luminance and color difference) color space by the JPEG (Joint Photographic Experts Group) scheme is well known.
Image processing based on JPEG will be briefly described below with reference to FIG. 1.
FIG. 1 is a block diagram for attaining image compression processing based on JPEG.
Input image data is divided into (8xc3x978) pixel blocks by a block forming processing unit 101.
The divided image data blocks are DCT (Discrete Cosine Transform)-transformed by a DCT transform processing unit 102. The DCT-transformed image data blocks are quantized based on a predetermined quantization step in a quantization processing unit 103, and the quantized blocks are Huffman-encoded by a Huffman encoding processing unit 104.
With the above-mentioned processing, the image data can be compressed to about {fraction (1/10)} without making its image quality deterioration conspicuous.
The encoded image data may often be subjected to spatial filtering processing or contrast processing for image display or the like, or pixel density conversion processing for converting the data into a desired resolution or size.
Conventionally, the spatial filtering processing, contrast processing, and pixel density conversion processing are performed for R, G, and B signals as primary color signals.
Therefore, when the filtering processing or pixel density conversion processing is performed by the conventional method for the image data compression-encoded in the YUV color space by JPEG, or when compression encoding in the YUV color space like JPEG is performed for image data subjected to the filtering processing or pixel density conversion processing by the conventional method, a color space conversion processing unit for converting image signals of the primary color system (R, G, and B signals) into image signals of the color difference system, or vice versa, and an image processing unit for filtering processing are required for each color signal, resulting in complex processing.
Furthermore, in order to attain high-quality resolution conversion, a further complex arrangement is required.
Therefore, a long processing time is required when such processing is realized by software, or the circuit scale increases when it is realized by hardware, resulting in high cost.
It is an object of the present invention to provide, in consideration of the above-mentioned situation, an image processing apparatus and method which can realize simple image processing for already encoded color image data within a short period of time.
In order to achieve the above object, according to one preferred aspect of the present invention, an image processing apparatus and method are characterized in that color image data compression-encoded in the color difference system color space is input, the input color image data is decoded, luminance component data of the decoded color image data is subjected to correction processing, and the processed luminance component data and color difference component data of the decoded color image data are encoded.
According to one preferred aspect of the present invention, an image processing apparatus and method are characterized in that color image data compression-encoded in the color difference system color space is input, the input color image data is decoded, luminance component data of the decoded color image data is subjected to correction processing, and color space conversion is performed on the basis of the processed luminance component data and color difference component data of the decoded color image data.
It is another object of the present invention to provide an image processing apparatus and method, which can realize image processing and compression encoding of input color image data by simple processing within a short period of time.
In order to achieve the above object, according to one preferred aspect of the present invention, an image processing apparatus and method are characterized in that color image data is input, the input color image data is converted into data in the color difference system color space, luminance component data of the converted color image data is subjected to correction processing, and the processed luminance component data and color difference component data of the converted color image data are encoded.
It is still another object of the present invention to provide an image processing apparatus and method, which can realize high-speed pixel density conversion free from any deterioration of the image quality by changing the degree of image quality after conversion in units of components upon executing the pixel density conversion for color image data.
In order to achieve the above object, according to one preferred aspect of the present invention, an image processing apparatus and method are characterized in that color image data is input, first component data of the color image data is subjected to first pixel density conversion processing, second component data of the color image data is subjected to second pixel density conversion processing, and the first pixel density conversion processing can attain pixel density conversion with higher quality than that of the second pixel density conversion processing.
Other objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.